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CYA tests- interference?

Are there any tests that interfere or have to be accounted for when testing CYA? Like calcium, etc?

I tested the CYA of my dad's pool to be 160 ppm. I bumped the FC to 18 ppm, the target percentage, but it keeps dropping to 8-10 overnight and through the next day. No CC and the water is crystal clear, but it does have the pollen problem many others are reporting. I'm finding it hard to believe that it's losing 8-10 ppm of FC just to pollen, though. No one's been in the pool for a week.

When I took over, the pool guy had royally screwed up the pool, turned it to green soup, eventually replaced the water then let it go to. No idea what he'd been shocking with, but obviously dichlor as there is CYA (plus there was a case of it in my dad's shed which he's since returned), and I suspect he also added straight stabilizer. I'm now wondering if he also used cal-hypo and possibly it's accounting for some turbidity that I'm reading as CYA, and possibly the CYA isn't as high as I tested. Pool does appear clear though, you can easily see the bottom 4' down.

Just wondering. If it is really 160 CYA, then it's likely pollen that's eating the bleach. If it's not, then I'd like to know so I can quit donating bleach to the sun

John, I used a dillution then mulitplied by 2 to get the 160 CYA reading. His water isn't cloudy.

Something just occured to me that I had completely forgot about. I added 16 oz of poly to his 13,500 gal. I remember now that chem geek had said using poly burns up some of you chlorine. I don't use poly, so have no experience with it. Possibly this is what accounted for the big drop?

I assume the drop is a one time thing, until more poly is added, of course. I guess I should bump back to 18 ppm tonight and see where it's at tomorrow night.

Yes, if you recently added PolyQuat, then it will be at high levels and high chlorine levels will break it down, thus consuming lots of chlorine. The smaller polymer chains are still effective as an algaecide, but you are right that bringing the chlorine back up should have less reduction this time, unless you've got nascent non-visible algae or some other source of chlorine consumption.